P-Channel Mosfets getting very hot

[TechGuy]

Hi Guys,

I'm having some problems with my design, before i finalize it I have decided to do a quick hook up with wires to check if everything is working fine, basically I have and external source of the PWM signal ( just focus only to the first channel for now) it has a resistor divider each of 1K and a 10K in series, then feeded to the MC33926 which is actually a H-Bridge, Brushed DC Motor Driver, but i actually using it as a gate driver for my others mosfets P-Channel from Vishay, each channel should cope with more than 30A. However I feed my PWM signal and have to the output a nice inverted PWM signal ready to drive my Mosfets, and the first test I just tried a small load max 3.3A and the control was working fine and the mosfet was not getting hot at all, but when i switched load and not even too big a 5/6A the mosfet gets very very hot! and I cannot understand why? please find attached my schematic.

Any help would be really appreciated,

thanks

 

[Audioguru]

Your schematic shows NO supply voltages and also does not show the PWM frequency.

 

[crutschow]

A 25kΩ gate resistor will slow the turn-on and turn-off of the MOSFETs due to their gate capacitance, which causes high switching losses.
Why is that resistor such a high value?

 

[TechGuy]

Your schematic shows NO supply voltages and also does not show the PWM frequency.

Hi sorry you are right! Vin is 12V and pwm frequency is around 12.5KHz. But i sorted out, there was a problem with my connection, I connected the Vin of the MC33926 to the output of the mosfet instead to Vin..:bang: I should have checked the connections first.

I wanted to add to the motor control an overcurrent protection any suggestion? I was thinking a resettable fuse to each output or a circuit breaker, but i have some concerns about the time reaction of those two. would it be better considering to add a micro with some current sensing to each output and if is drawing more than it should turn off the mosfets?

thanks

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A 25kΩ gate resistor will slow the turn-on and turn-off of the MOSFETs due to their gate capacitance, which causes high switching losses.
Why is that resistor such a high value?

Hi actually is only 25 Ohm..! thanks for your for message.

 

[Audioguru]

Don't forget that a DC motor draws a HUGE current when it is stalled. It is stalled when it starts running and when something stops it when it is running.

 

[TechGuy]

Don't forget that a DC motor draws a HUGE current when it is stalled. It is stalled when it starts running and when something stops it when it is running.

What are you suggesting? any advise for over-current protection?

thx

 

[Audioguru]

Allow for the very high starting current and the very high stalled current if you limit the current. Maybe make a timer to allow the very high current before the current limiting works.